Multistate differential transmission

ABSTRACT

A torque feedback multistate transmission employing an adjustable differential transmission with one or more planetary gear systems for providing improved efficiency under stationary load conditions and infinitely variable output during each state of the transmission. In one embodiment there is provided a pair of planetary gear systems, a reversing mechanism, a first transmission to establish the state, and a second transmission to provide continuous power flow during shifting of the first transmission. A differential transmission provides continuous variable output during each state of the multistate transmission.

BACKGROUND OF THE INVENTION

This invention relates to a torque feedback transmission and moreparticularly to a torque feedback transmission with direct couple bypassutilizing operational clutches.

In my patent application entitled "Torque Feedback Transmission" havingSer. No. 649,691 filed on Sept. 12, 1984, now U.S. Pat. No. 4,637,275,issued on Jan. 20, 1987, there is disclosed and claimed a torquefeedback transmission capable of providing perfect coupling betweeninput and output torque and speed without the need for clutching andshifting mechanisms.

In some systems, the output of the hydrostatic transmission is connectedeither directly, or by fixed gear ratio transmission, to the outputshaft. In such a design the rotor of the motor is stationary when theoutput shaft is stationary. In order to apply a load to the outputshaft, sufficient force must exist to overcome the static friction ofboth the hydraulic motor and the load. In addition, some types of pumpsoperate inefficiently when they bear a stationary load. In the torquefeedback design covered in my aforementioned application, the hydraulictransmission bears only the static friction of the load.

Also, some types of differential units, such as differential cones, canonly provide infinite variation over some fixed gear ratio and cannot bedirectly coupled to a stationary load, whereas, by use of the torquefeedback design in my above mentioned application it is possible tocouple such devices to a stationary shaft without the use of a clutch,and furthermore, for each state or set of gear ratios, the differentialunit may be designed to experience its full range of motion thusresulting in a maximum torque reduction.

In the aforementioned application, a variety of embodiments aredisclosed in which a differential unit comprising a fixed displacementhydraulic pump and a variable displacement hydraulic motor are coupledto adjust the torque feedback and accomplish the purposes of theinvention. Several of the embodiments disclosed in the applicationprovide for a partial bypass of the differential unit in order to reducefluid pressures in the pump. Such pressures are of special concern atlow speeds and under starting conditions.

In one embodiment of the aforementioned application, there is discloseda torque splitting arrangement wherein the differential unit is bypassedin such a way that there is a direct coupling from the input to the loadof a portion of the torque supplied. In that arrangement, it can be seenthat when a stationary load exists at the output shaft all power mustflow through the hydrostatic or differential unit, with the accompanyinghigh fluid pressures in the unit and in many cases, depending on thetype of pump employed, reduced efficiency.

SUMMARY OF THE INVENTION

In the present invention, the drawback of the torque splittingarrangement described above is overcome by a torque feedbacktransmission in which some of the power is delivered directly to theoutput shaft and is provided with operational clutches to reduce thetorque which appears at the differential unit throughout its entirerange of operation. In addition, it is not a necessary part of thistorque reduction that the input to the hydrostatic unit rotate at ahigher speed than the input shaft. Furthermore, for each state or set ofgear ratios, the differential unit experiences its full range of motionthus resulting in a maximum torque reduction.

It is thus an object of this invention to provide a multistatedifferential transmission with reduced loading on the differential unit.

Other objects and advantages of this invention will hereinafter beobvious from the following description of preferred embodiments of thisinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in partially schematic form a three statetransmission incorporating the principles of this invention.

FIG. 2 is a clutch engagement diagram for the transmission of FIG. 1.

FIG. 3 is a section and partially schematic view of the reversingmechanism shown in FIG. 1.

FIG. 4 is a section and partially schematic view of transmission 94shown in FIG. 1.

FIG. 5 is a section and partially schematic view of transmission 142shown in FIG. 2.

FIG. 6 is a partially schematic view in section of an alternativeembodiment of this invention.

FIG. 7 is a modification of the transmission shown in FIG. 6.

FIG. 8 shows another embodiment of a multistate transmission using tworeversing mechanisms.

FIG. 8a is the clutch engagement diagram for the transmission shown inFIG. 8.

FIG. 9 shows a simpler version of the transmission illustrated in FIG.8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, transmission 10 is a three state or speed machinewhich has an input shaft 12 connected to a prime mover 13 and an outputshaft 14 connected to a load (not shown).

Input shaft 12 is keyed to a pinion 16 and also connected to the rightside of operational clutch 18. Connected also to the right side ofclutch 18 is a shaft 22 which is connected to planetary gear carrier 24in planetary gear train 26. Thus, depending on the transmission ratio aswill be later described, input power to transmission 10 is split betweenpinion 16 and carrier 24 in planetary gear train 26.

Pinion 16 is engaged with a gear 28 mounted on and keyed to a shaft 32on which is mounted and keyed gears 34, 36, and 38. Some of the inputpower transferred by pinion 16 flows into a planetary gear train 42 byway of gear 38 engaged with gear 44 which is connected to ring gear 46of train 42. The torque applied to ring gear 46 causes a reaction torqueto appear at sun gear 48 through planetary gears 52. A shaft 54 joinssun gear 48 to a clutchable, reversing mechanism 56. The output oftransmission 10 is delivered by planetary gear carrier 58 supportingplanetary gears 52 to output shaft 14.

The direction of flow of power by way of shaft 54 depends on thedirection of rotation of sun gear 48. When sun gear 48 rotates in theopposite direction to that of ring gear 46, which would be the case whenoutput shaft 14 is stationary, then sun gear 48 drives shaft 54. Whensun gear 48 rotates in the same direction as ring gear 46, then shaft 54will be driving sun gear 48.

The reason for this reversal of power flow is that the torque arisingfrom sun gear 48 in reaction to the torque applied to ring gear 46 is inthe same direction as the latter torque, independent of the direction ofrotation of sun gear 48. Since power is equal to the product of torqueand rotational velocity, and since only the direction of rotationalvelocity changes, then the flow of power reverses around the point ofzero velocity for sun gear 48. The purpose of reversing mechanism 56 andits internal structure will be described later.

Planetary gear train 26 is a torque splitting unit consisting ofplanetary gear carrier 24 supporting planetary gears 62 which areengaged with ring gear 64 and sun gear 66, the latter being connected toa shaft 68 for transferring its torque into differential unit 72. Whenclutch 8 is disengaged, ring gear 64 rotates free of shafts 12 and 22.The details of differential unit 72 will be described later.

Ring gear 64 is connected on one side to a gear 73 and on the other sideto the left side of clutch 18 by way of a hollow shaft 74. Ring gear 64is also joined to output shaft 14 by way of gears 73, 76, a shaft 78connected to the right side of clutch 82, a shaft 84 connected to theleft side of clutch 82, and a gear 86 engaged with gear 88 mounted onand keyed to output shaft 14.

When clutch 82 is engaged, and clutch 18 disengaged, input power issplit so that some of it is delivered directly to output shaft 14. Thespeed of ring gear 64 will be directly proportional to output shaft 14due to the direct mechanical connection. The gear ratio supplied bygears 88, 86, 76, and 73 determines at what fraction of the input speedof shaft 12 will sun gear 66 and ring gear 64 be rotating at the samespeed.

When clutch 82 is disengaged and clutch 18 is engaged, power is nolonger being split by planetary gear train 26 whose various parts arenow coupled together. As is seen in FIG. 2, clutches 18 and 82 arenormally in opposite states of engagement.

Referring to planetary gear train 42, it was noted that sun gear 48 isconnected by way of shaft 54 to reversing mechanism 56. Reversingmechanism 56 is connected by way of shaft 92 to transmission 94.

The purpose of reversing mechanism 56 is as follows: When shaft 54rotates in the opposite direction to that of input shaft 12, mechanism56 causes this direction to be reversed so that shaft 92 rotates in adirection opposite to that of shaft 54. When shaft 54 rotates in thesame direction as shaft 12, mechanism 56 does not reverse the directionof shaft 92 with respect to shaft 54, and hence shafts 54 and 92 rotatein the same direction, but not necessarily at the same speed. Thus,mechanism 56 either causes shafts 54 and 92 to rotate together in thesame direction or in opposite directions. As will be seen from thediscussion below, reversing mechanism 56 reverses in states one and two,and locks up shafts 54 and 92 in the same direction of rotation in statethree.

From shaft 32, gear 36 drives a gear 96 which is connected totransmission 94 through a hollow shaft 98 so that transmission 94receives power from both shafts 92 and 98.

The purpose of transmission 94 is to provide for a clutchable couplingbetween shafts 92 and 98. Power flows straight through transmission 94as shaft 92 is always coupled to the former's output shaft 102; however,the speed ratio between shafts 92 and 102 may be altered depending onthe speed ratio within transmission 94 as will be later described.Transmission 94 permits power flow through transmission 10 while thelatter is in the process of shifting from one state to another by virtueof coupling shafts 92 and 98 together during shifting as will be seenfrom the discussion below. The shifting periods are indicated byasterisks (*) in FIG. 2.

The torque on shaft 102 is transferred to power return unit 104 by wayof spur gears 106 and 108, shaft 112, and spur gears 114 and 116 througha hollow shaft 118.

The purpose of power return unit 104, about to be described, exceptduring lockup of transmission 10 to be later described, is to change thespeed of sun gear 48 in planetary gear train 42 so as to change thespeed of output shaft 14 over a specific range during each state oftransmission 10.

Power return unit 104 consists of a planetary gear train here shown as apair of bevel gears 122 mounted for independent rotation on the ends ofa carrier shaft 124 which is supported by carrier 126, the latter beingconnected by way of a hollow shaft 128 to the left side of anoperational clutch 132.

Engaged with bevel gears 122 are a bevel gear 134 connected to hollowshaft 118 and a bevel gear 136 connected to a shaft 138 which is joinedto the right side of operational clutch 132. A shaft 139 rotating insideof hollow shaft 118 is pinned at one end to and driven by carrier shaft124 and provides at its other end input to a transmission 142. Theoutput of the latter is delivered by way of a shaft 144 to shaft 32 byway of a spur gear 146 engaged with gear 34. Transmission 142 is amultispeed speed transmission which provides positive coupling betweenshaft 32 and carrier shaft 124 of power return unit 104. The purpose oftransmission 142 is to establish the three states or speed ranges oftransmission 10.

A shaft 148 delivers the output of differential unit 72 to the rightside of operational clutch 132 and thus is directly coupled at all timesto shaft 138 which is connected to bevel gear 136 in power return unit104.

It is thus seen that bevel gear 134 is tied directly to output shaft 102of transmission 94, and bevel gear 136 is tied directly to the output ofdifferential unit 72.

Differential unit 72 in this embodiment consists of a hydrostatic unitwhich contains a variable displacement hydraulic pump 151 coupledhydraulically to a fixed displacement hydraulic motor 152. Thedisplacement volume of pump 151 is controlled by a control member 151a.Motor 152 is connected to shaft 148 delivering the output of unit 72,while the rotor of pump 151 is connected to shaft 68 which supplies theinput to the former. Adjustment of control member 151a alters the outputspeed and torque of the transmission 10 over the range of the latter inthe state in which it is operating. The construction, operation andcontrol of unit 72 is well known in the art and further descriptionherein of its details of construction is not necessary for anunderstanding of this invention. Its function in transmission 10 will bemore particularly described further below.

As noted above, transmission 10 is a three speed device and a morecomplete understanding of its operation can be understood by referringto FIG. 2 in connection with the discussion of FIG. 1.

The operation of transmission 10 is described with input shaft 12connected to prime mover 13 which is operating at a constant rotationalspeed so that the speed of shaft 12 is constant.

With output shaft 14 stationary, that is, the load not being moved, andtransmission 10 in state one, sun gear 48 will rotate at a speed greaterthan ring gear 46 driving shaft 54, and its direction of rotation willbe opposite to that of input shaft 12. Transmission 94 is initially in adisengaged state, that is, shafts 92 and 98 are decoupled which allowspower to flow (and torque to be transferred) from shaft 92 to shaft 102and bevel gear 134 in power return unit 104. The speeds of shafts 92 and102 are equal. The torque on gear 134 causes a reaction torque to appearat bevel gear 136 equal to the torque applied to gear 134. (They areequal only because both gears are the same size. The reaction torquewhich appears at gear 136 is countered by the torque supplied bydifferential unit 72 via shafts 138 and 148. In this state, clutch 132is disengaged so that carrier 126 in unit 104, attached to shaft 124, isnot coupled to shafts 138 and 148, and gear 136 is stationary.

For power return unit 104 constructed as shown, the equations of motionare: W₁ =1/2 (W₂ +W₃) where W₁ equals the speed of carrier shaft 124, W₂equals the speed of gear 134, and W₃ equals the speed of gear 136.Therefore, with W₃ equal to zero, W₁ equals 1/2 W₂.

Transmission 10 is now brought out of neutral by adjusting controlmember 151a in differential unit 72 to increase the displacement of pump151 so that gear 136 starts to rotate in the same direction as gear 134and carrier shaft 124. The speed of carrier shaft 124 is fixed by thegear ratio within transmission 142 due to direct coupling to shaft 32.As the speed of gear 136 increases, the speed of gear 134 decreaseswhere W₂ =2W₁ -W₃ (initially W₂ =2W₁). This results in a reduction inspeed of sun gear 48 and shaft 14 starts to move the load. Control lever151a is moved until W₃ and the speed of shaft 14 reach some maximumvalue in state one of transmission 10. If the initial speed of gear 134is much greater than the maximum value of gear 136 obtained fromdifferential unit 72 this process is repeated until the final speed ofgear 134 equals zero.

In order for gear 136 to be returned to zero speed (thus to permitincrease in the speed of output shaft 14), transmission 142 must shift,to cause shaft 124 to rotate at a new speed. While transmission 142 isshifting, however, transmission 94 is first actuated to cause shafts 92and 98 to be coupled together. During this transition coupling periodall power flows directly from shaft 32 to output shaft 14 by way ofplanetary gear train 42. Power return unit 104 during this transitionperiod is completely bypassed allowing for the shifting of transmission142. It should be noted that transmission 94 allows shafts 92 and 102 tobe coupled to shaft 32 at different speed ratios depending on whethertransmission 10 is going from state one to state two, or state two tostate three, thus allowing for continuous power transfer as the machinegoes from one state to the next. As previously noted, the use of anasterisk (*) in FIG. 2 designates the transition periods just described.Blank spaces indicate a "do not care" status. Details of theconstruction and operation of transmissions 94 and 142 will be givenlater.

To illustrate more clearly the operation described above, consider thefollowing situation: Suppose sun gear 48 is one half the radius of ringgear 46. When output shaft 14 is stationary, gear 48 rotates at twicethe speed of ring gear 46 and in the opposite direction. Reversingmechanism 56 causes the direction of motion of shaft 54 to be reversedresulting in shaft 92 to rotate in the opposite direction of shaft 54but in the same direction as ring gear 46. With W₄ equal to the speed ofgear 46 and W₅ equal the speed of sun gear 48, then as stated above, W₄=-1/2W₅ and also the speed of shaft 92 equals 2W₄ or -W₅. Transmission94 has shafts 32 and 92 decoupled and shafts 92 and 102 rotatingtogether. Gear 134 then rotates at speed 2W₄. Note that W₄ also equalsthe speed of input shaft 12 and -W₄ the speed of shaft 32.

Initially gear 136 is at rest and so carrier shaft 124 rotates at speedW₄ and is coupled to shaft 32 via transmission 142 at 1:1 ratio. Unit 72is now operated by moving control member 151a so that gear 136 increasesin speed. The speed of carrier shaft 124 is fixed because of itsmechanical coupling via transmission 142. Therefore, as gear 136increases in speed, gear 134 decreases and so does sun gear 48,resulting in movement of output shaft 14 and its increase in speed.

When gear 136 reaches speed W₄ then gear 134 has declined in speed alsoto W₄. At this point gear 48 rotates at -W₄. Because gear 48 is 1/2 theradius of gear 46 in this embodiment, the equation of motion forplanetary unit 42 is Wo=2/3 W₄ +1/3 W₅ where Wo is the speed of outputshaft 14. W₅ equals -W₄ so, Wo=1/3 W₄ or 1/3 the input speed.

To further increase the speed of output shaft 14, transmission 10 mustnow pass from its first state just described to its second state. Thisis initially accomplished as already noted by first causing transmission94 to couple shafts 32 and 92, that is, to become engaged and to movetransmission 142 into neutral so that shafts 124 and 32 are decoupledfrom each other. During this momentary period of engagement oftransmission 94, shaft 92 rotates at the same speed as shaft 32 so thecoupling is one to one. While transmission 94 is so engaged, all thepower flowing through transmission 10 passes by way of transmission 94to output shaft 14, hence, the load is removed from transmission 142 andunit 72.

To move transmission 10 into state two, with transmission 94 momentarilyengaged to couple shafts 92 and 98, and transmission 142 momentarilydisengaged to decouple carrier shaft 124 from shaft 132, as describedabove, control member 151a in differential unit 72 is returned to itsinitial position (i.e., minimum displacement within the hydraulic pump).Transmission 142 is moved into its next speed so that the speed ofrotation of carrier shaft 124 is reduced by half.

Transmission 94 is then disengaged and transmission 142 is engaged, withthe result that carrier shaft 124 now rotates at a new speed which, forthe example given above, equals 1/2 W₄, in other words one half thespeed during state one with control member 151a in its initial position.

The situation is repeated with unit 72 causing gear 136 to increase inspeed until it equals W₄. Since carrier shaft 124 rotates at 1/2 W₄,this will force gear 134 to come to rest. In addition, sun gear 48 willalso be at rest. In order to move into state three of transmission 10,transmission 94 is momentarily engaged holding sun gear 48 stationarywhile transmission 142 and unit 72 move to the next or third state.Transmission 142 is moved to neutral but this time clutch 132 is nowengaged causing carrier shaft 124, gear 136 and gear 134 to rotate as asingle unit. In addition, reversing mechanism 56 is now moved to a statewhere shafts 54 and 92 rotate together. Thus, in the third state oftransmission 10, both transmission 94 and 142 are disengaged and unit 72is effectively coupled directly to sun gear 48.

As the speed of shaft 148, the output of unit 72, increases, so does thespeed of sun gear 48 until it reaches W₄ and then the output shaft 14will rotate at the speed of input shaft 12. At this point, withtransmission 10 in its third state and output shaft 14 running at thesame speed as input shaft 12, a lockup condition can be produced byactuating transmission 94 to engage shafts 92 and 98 thereby couplingshaft 32 directly to shaft 102.

As seen in FIG. 3, reversing mechanism 56 consists of a carrier 302connected on one side by way of an operational or free wheeling clutch304 to stationary housing 306 of transmission 10. The other side ofcarrier 302 is connected to a sliding dog or any type of an operationalclutch 308 which can be locked to output shaft 92. Input shaft 54 isconnected to bevel gear 312 joined by planetary gears 314 to bevel gear316 connected to output shaft 92. Planetary gears 314 rotate on shafts317 attached to carrier 302.

When clutch 304 is disengaged and clutch 308 engaged then shafts 54 and92 are locked together and rotate at the same speed. When clutch 304 isengaged and sliding dog clutch 308 is disengaged then shaft 92 rotatesin the opposite direction to that of shaft 54. If both clutches areengaged then shafts 54 and 92 will be stationary. Because reversingmechanism 54 in this embodiment has sun and ring gears of equal radii,the equation of motion is W_(c) =1/2 W_(r) +1/2 W_(s) where W_(s) is thespeed of gear 312, W_(r) is the speed of gear 316, and W_(c) equals thespeed of carrier 302. If carrier 302 is held stationary, then 0=1/2W_(r) +1/2 W_(s) or W_(s) =-W_(r).

If W_(c) is then locked to either W_(r) or W_(s) then W_(s) =1/2 W_(r)+1/2 W_(s), or W_(r) =W_(s). As previously noted, and as seen in FIG. 2,reversal takes place in the first two states of transmission 10 andlock-up in the same direction in the third state.

For details of transmission 94, reference is made to FIG. 4.Transmission 94 contains a clutch 402 which couples shaft 92 to hollowshaft 98 and gear 96 when engaged. The ratio of this coupling isdetermined by sliding clutches 404 and 406 and gears 408 and 412, 414and 416, and 418 and 422. Gear 96 is connected to gear 422 by way ofhollow shaft 98. Transmission 94 is of conventional design and itsconstruction and operation are well known in the art. Also, transmission94 can be of the type described or may be designed to supply more gearratios or less depending on the requirements of transmission 10.

Transmission 142 may be a conventional sliding clutch controlled threespeed transmission as illustrated in FIG. 5. Briefly described, it isprovided with its input shaft 139 and output shaft 144 with slidingclutches 502 and 504 to provide for three gear ratios as a result of theway gears 506, 508, 510, 512, 514, and 516 are joined to each other asillustrated.

By way of example, suppose differential unit 72 has a range of motionfrom 0 to W_(i), the input speed of shaft 68. To avoid increasing thecomplexity of the problem, assume shaft 68 directly connected to shaft22 and input shaft 12. For a three state machine, as illustrated in FIG.1, the radius of ring gear 46 in planetary gear system 42 is twice thatof sun gear 48. Therefore, the equations of motion for planetary geartrain 42 is W_(c) =2/3 W_(r) +1/3 W_(s) where W_(c) is the speed ofcarrier 58 (it is also the output speed of transmission 10), W_(r) thespeed of ring gear 46 and W_(s) the speed of sun gear 58. For thisexample, W_(r) =W_(i), or W_(r) equals the input speed. The tranmissionis initially in state one. When W_(c) =0, then W_(s) =-2W_(r). In stateone, reversing mechanism 56 causes shafts 54 and 92 to rotate inopposite directions. Since shaft 54 is connected to sun gear 48, theinitial speed of shaft 92 will be 2W_(r) or 2W_(i). As previouslydescribed, this speed is imparted to bevel gear 134 of power return unit104. Initially, bevel gear 136 is at rest. As previously noted, theequation of motion for unit 104 is W₁ =1/2 W₂ +1/2 W₃ or 2W₁. This 1:1ratio between shaft 32 and carrier 126 is supplied by transmission 142.Control member 151a is moved causing unit 72 to experience its fullrange of motion. Therefore, at the end of state one, gear 136 rotates aW_(i). The speed of gear 134 equals 2W_(i) -W₃. Since W₃ =W_(i), thespeed of gear 134 equals W_(i) also. As a result, the speed of sun gear48 is -W_(i) (reversing mechanism 56 causes shafts 92 and 54 to rotatein opposite directions). Therefore, W_(c) =2/3 W_(i) -1/3 W_(i) or W_(c)=1/3 W_(i) at the end of state one.

It is a feature of this transmission that unit 72 experiences its fullrange of motion (zero to W_(i)) in each state. Hence, as transmission 10shifts to state two, transmission 142 shifts so 2W_(i) =W₂ +W₃ with W₃=0 and W₂ =W_(i). In state two, W₁ =1/2 W_(i). At the end of state two,W₃ once again equals W_(i). Solving for W₂, W₂ =2 (1/2W_(i))- W_(i) orW₂ =0. This also means that W_(s) =0 and therefore W_(c) =2/3 W_(i) atthe end of state two.

In state three, as earlier noted, reversing mechanism 56 is shifted tolock shafts 54 and 92. Clutch 132 is engaged and transmission 142 isshifted to neutral allowing carrier 126 to rotate independently of shaft32 and shafts 138 and 128 to rotate together. At this point, the outputof unit 72 and the speed of sun gear 48 are equal. As sun gear increasesfrom zero to W_(i), W_(c) increases speed from 2/3 W_(i) to W_(i).

Reversing mechanism 56 can be any kind of epicyclic gear train, justlike unit 46. Different combinations of epicyclic (planetary) geartrains can be used to achieve different load torque reductions for eachstate.

The three state transmission 600 shown in FIG. 6 is similar in designand operation to the transmission described in FIG. 1. The exceptions inconstruction are as follows: Planetary gear unit 602 consisting of ringgear 604, sun gear 606, planetary gears 607, and planetary carrier 608has power supplied to it via hub gear 612. Shaft 614 is the outputshaft. Ring gear 604 is keyed to shaft 614. In this transmission theneed for a reversing mechanism has been eliminated because sun gear 606initially rotates in the same direction as ring gear 604. The purpose ofthe three states of this transmission is to cause the speed of sun gear606 to decline with the result that ring gear 604 will increase inspeed. The operation of transmissions 616 and 618, power return unit622, and differential unit 624 are identical to units 94, 142, 104 and72, respectively, described for the transmission in FIG. 1, with unit616 engaging while units 618 and 624 shift.

Torque splitting planetary unit 626 receives all the power from inputshaft 628. In FIG. 1 only part of the input power flows throughplanetary unit 26. (Either arrangement may be used in eithertransmission.) An alternative coupling arrangement is employed forlocking up mechanically the torque splitting unit 626. This isaccomplished through gears 632, 634, 636, and 638. Gears 636 and 634 arejoined by shaft 642 and clutch 644. When clutch 644 is disengaged andclutch 646 engaged, the power supplied at shaft 628 is split. Whenclutch 644 is engaged and clutch 646 disengaged, no power splittingoccurs. This arrangement also suggests the possibility of adding atransmission 650 along with differential unit 624 as shown in FIG. 6abetween break lines A and B. The purpose of this would be to allow forincreased loads or reduced levels of power through various states ofoperations. Without transmission 650 the load torque reduction whichappears at differential unit 624 is constant for all states.

FIG. 8 illustrates an embodiment of a multistate device using tworeversing mechanisms which is easier to design in a colinearconfiguration. The device illustrated is a four state machine 800comprising a pair of units 802 and 804 for load torque reduction. Unit802 comprises a common ring gear 806 shared between a torque reducingplanetary gear train consisting of planetary gears 808 connected by wayof carrier 810 to output shaft 812 and a reversing planetary gear trainhaving planetary gears 814. Sun gears 816 and 818 are connectedrespectively to shaft 820 and hollow shaft 822. Carrier 824 is keyed tofree wheeling clutch (FWC) 826. FWC 826 is supported by transmissionhousing 828. Carrier 824 terminates into one side of operational clutch830. The other side of operational clutch 830 is keyed to hollow shaft822. Hollow shaft 822 is also keyed to carrier 832 in planetary geartrain 804. It can be seen that the planetary gear train consisting ofsun gear 818, ring gear 806, and planetary gears 814 act as a reversingmechanism. When operational clutch 830 is engaged, carrier 824, sun gear818, and ring gear 806 rotate at the same speed. In addition, the torqueappearing on ring gear 806 from the load applied to shaft 812 appearswithout reduction at hollow shaft 822 as opposed to the reduction whichresults when clutch 830 is disengaged.

Planetary gear train 804 is identical in construction to unit 802 exceptthat the FWC has been replaced with an operational clutch 834.Operational clutch 834 is connected between transmission housing 828 andplanetary carrier 835 which is connected to one side of the secondoperational clutch 836. The flow of power into or out of unit 804 viacarrier 832 and shaft 822 depends on the state of unit 802. Operationalclutches 830, 834 and 836 cause transmission 800 to change states. Ifclutches 830 and 834 are disengaged, a mechanical neutral exists, if allare engaged, the transmission is locked up.

Planetary gear train 804 consists of a common ring gear 838 engaged withtwo sets of planetary gears 840 and 842, and a pair of sun gears 844 and846, respectively. Sun gear 844 is joined to sun gear 816 of unit 802 byshaft 820 passing through hollow shaft 822 and to a spur gear 848 by ashaft 850. Sun gear 846 is connected through hollow shaft 852 to a spurgear 854 which is connected through spur gear 856 and to shaft 858 whichis the output of differential unit 860 having a control member 860a. Thelatter unit is identical to differential unit 72 shown in FIG. 1. Inputshaft 862 to differential unit 860 is connected by way of spur gears 864and 848 to shaft 850 and shaft 866 which is the input shaft totransmission 800.

Input to transmission 800 is split, in the fourth or final state of thetransmission, between differential unit 860 and sun gears 816 and 844,the latter two sun gears being directly connected to each other. Theoutput of differential unit 860 is connected to sun gear 846 in unit804. Operation of transmission 800 is described completely in the clutchengagement diagram shown in FIG. 8a.

The device shown in FIG. 8 represents a multistate device using onlytorque splitting and reversing mechanisms. The design can be madecompact because the two planetary gear trains as illustrated can shareeither a common ring gear or a common sun gear.

It was mentioned earlier that the reversing mechanism can be any kind ofepicyclic gear train and that different combinations of such gear trainscan be used to obtain different load torque reductions for each state.This is illustrated by the device 900 shown in FIG. 9, consisting of aplanetary gear train 902, a reversing mechanism 904, and a differentialunit 906, in effect a simpler version of the transmission shown in FIG.8.

Planetary gear train 902, constructed of bevel gears, has an equation ofmotion: W_(c) =1/2 W₁ +1/2 W₂ where W_(c) is the speed of output shaft908, W_(i) equals the input speed of shaft 910, W_(i) and W₂ the speedof shaft 906. The device in FIG. 9 is a two state machine. When W_(c)equals zero, W₂ =-W₁ or W_(i) since W₁ =W_(i). Reversing mechanism 904is identical in construction to the device shown in FIG. 3. In stateone, reversing unit 904 causes shafts 912 and 914 to rotate in theopposite direction. Initially, shaft 914 equals at -W_(i) and throughoutstate one, shaft 914 rotates at -W₂. The speed of shaft 914 declines tozero at the end of state one. At this point, shaft 912 is alsostationary and the speed of output shaft 908 is 1/2 W_(i). In state twothe device in FIG. 9 behaves exactly like transmission 10 (FIG. 1) instate three. Reversing unit 904 changes state at the beginning of statetwo when W₂ still equals zero, locking shafts 912 and 914 together. Instate two the output of unit 906, that is, shaft 914, increases in speedfrom zero to W_(i) causing W₂ to increase in speed from zero to W_(i)also. When the output of unit 906 equals W_(i) output shaft 908 equalsW_(i) at the end of state two. Input is at shaft 910.

In the most general case, the reversing mechanism illustrated in FIG. 3may be constructed with any type of planetary unit. If planetary geartrain 902 is changed so that its new equation of motion is W_(c) =1/3 W₁+2/3 W₂ (W₁ and W₂ same as before) then for W_(c) =0, W₂ =-1/2 W₁ or-W_(i). Reversing unit 904 can be changed by using a gear train whoseequation of motion is W_(c) =2/3 W₂ +1/3 W₃ where W₃ is the speed ofshaft 14 and W₂ the speed of shaft 912. In state one W_(c) is zero andW₃ =-2W₂. With shaft 908 stationary, W₂ =-1/2 W_(i) and W₃ =W_(i). Instate one reversing unit 904 provides a reduction in load torque of onehalf. Gear train 902 provides a load torque reduction of 2/3. Thiscombined with (1/2) for reversing unit 904 the total load torquereduction is (1/2) (2/3) or 1/3 for state one. In state two the loadtorque reduction is 2/3 because the 1/2 reduction supplied by reversingunit 904 in state one is absent in state two because shafts 912 and 914are locked together.

In FIG. 6 no reversing mechanism is needed. In the devices described inFIGS. 8 and 9, the power flow through the differential unit will be inboth directions. The device in FIG. 1 is a hybrid of the transmissiontypes illustrated in FIGS. 6 and 8 and contains both a reversingmechanism and a power return unit.

While only preferred embodiments of this invention have been described,it is understood that many variations of this invention are possiblewithout departing from the principles of this invention as defined inthe claims which follow.

What is claimed is:
 1. A multistate transmission having an input shaftand an output shaft comprising:a. planetary gear train means having aring gear, planetary gears with a planetary gear carrier, and a sungear, said planetary gear train means connected to said output shaft: b.first bypass means connecting said input shaft to said planetary geartrain means; c. differential transmission means for receiving its inputfrom said input shaft and having means to adjust the torque and speedoutput infinitely variable over its range of operation for each state ofsaid transmission; d. power return means for receiving the output ofsaid differential transmission means; e. means including clutch operatedspeed reversing means for interconnecting said sun gear in saidplanetary gear train means with said power return means; f. said powerreturn means including a first gear to receive the output of saiddifferential transmission means, a second gear connected through saidinterconnecting means to said sun gear, carrier gear means forinterconnecting said first and second gears supported for rotation on acarrier shaft, and means for supporting said carrier shaft for radialrotation; g. first multispeed transmission means connecting said meansfor supporting said carrier shaft to said first bypass means whereby therotational speed of said carrier shaft is determined as a fraction ofthe speed of said input shaft, whereby an increase in the output speedof said differential transmission means will cause a change in the speedof said sun gear causing said output shaft to increase in speed; h.means to shift the state of said multistate transmission when themaximum speed of the output shaft is reached for the existing state ofsaid multistate transmission comprising means to unload said firstmultispeed transmission means and bypass said power return means duringshifting of the latter from one speed to another; and i. means toprovide direct coupling between said input shaft and said output shaftthrough said planetary gear train means while said first multispeedtransmission means is shifting from one speed to another.
 2. Thetransmission of claim 1 in which said unload means to provide directcorepling includes a second multispeed transmission means to connectsaid bypass means to said sun gear.
 3. A multistate transmission havingan input shaft and an output shaft comprising:a. first planetary geartrain means having a ring gear, planetary gears with a planetary gearcarrier, and a sun gear, said planetary gear carrier connected to saidoutput shaft; b. first bypass means connecting said input shaft to thering gear in said first planetary gear train means; c. differentialtransmission means for receiving its input from said input shaft andhaving means to adjust the torque and speed output infinitely variableover its range of operation for each state of said transmission; d.power return means for receiving the output of said differentialtransmission means; e. means comprising a clutch operated reversingmechanism for interconnecting said sun gear in said first planetary geartrain means with said power return means so that the direction of torquesupplied to said power return means is in one direction regardless ofthe direction of rotation of said sun gear; f. said power return meansincluding a first gear to receive the output of said differentialtransmission means, a second gear connected to the output of saidreversing mechanism, carrier gear means for interconnecting said firstand second gears supported for rotation on a carrier shaft, means forsupporting said carrier shaft for radial rotation, and first multispeedtransmission means connecting the latter to said first bypass meanswhereby the rotational speed of said carrier shaft is determined as afraction of the speed of said input shaft, whereby an increase in theoutput speed of said differential transmission means will cause a changein the speed of said sun gear causing said planetary gear carrier insaid first planetary gear system and hence said output shaft to changein speed; and g. means to shift the state of said multistatetransmission when the maximum speed of the output shaft is reached inthe existing state of said multistate transmission comprising means tounload said first transmission means during shifting from one speed toanother and at the same time providing for a continuous flow of powerfrom said input shaft to said output shaft.
 4. The transmission of claim3 in which said unload means includes a second multispeed transmissionmeans to connect said bypass means to said sun gear through said firstplanetary gear train.
 5. The transmission of claim 4 having secondbypass means for delivering power from said input shaft to said outputshaft including second planetary gear train means having the planetarycarrier thereof connected to said input shaft and sun gear connected tothe input of said differential transmission means, first clutch meansbetween said input shaft and the ring gear of said second planetary geartrain means, and second clutch means between the ring gear of saidsecond planetary gear train means and said output shaft, said first andsecond clutch means always being in opposite states of engagement. 6.The transmission of claim 5 in which said first clutch means isdisengaged when said transmission is in its first state and is engagedwhen said transmission is in its second state.
 7. The transmission ofclaim 6 in which said differential means includes a variabledisplacement hydraulic pump receiving the input of said differentialmeans, and a constant displacement hydraulic motor energized by saidpump for delivering the output of said differential means, said means toadjust the torque and speed output during each state of said multistatetransmission being the means to adjust the displacement of saidhydraulic pump.
 8. The transmission of claim 6 in which said firsttransmission means has multiple speeds to correspond to the multiplestates of said transmission.
 9. The transmission of claim 8 having thirdclutch means between the output shaft of said differential means andsaid carrier shaft in said power return means, said third clutch meansbeing engaged during state three of said transmission so as to lock upsaid power return means with the sun gear in said first planetary geartrain means.
 10. The transmission of claim 9 in which said power returnmeans in which said first and second gears are bevel gears, and saidcarrier gear means includes planetary bevel gears joining said first andsecond gears, said planetary bevel gears being mounted on the ends ofsaid carrier shaft for both axial and radial rotation, and a carrierjoining said carrier gears and shaft for rotation, and means joiningsaid carrier to said third clutch means whereby when the latter isengaged said multistate transmission is in a lockup condition.